Radio communication system, radio base station apparatus, user terminal and radio communication method

A radio base station apparatus in a radio communication system comprising the radio base station apparatus to than a cell and user terminals to establish radio connection with the radio base station apparatus, the radio base station apparatus comprising:

• an array antenna having a plurality of antenna elements that are arranged in one direction;
• a selection section configured to select precoding vectors from a codebook that is set in advance to be uneven with respect to the direction of the arrangement of the antenna elements, based on communication quality information of the user terminals in the cell;
• a precoding multiplication section configured to multiply signals to supply to each antenna element by the selected precoding vectors;
• and
• a transmission section configured to transmit the signals multiplied by the precoding vectors to the user terminals.

A user terminal in a radio communication system comprising a radio base station apparatus to form a cell and user terminals to establish radio connection with the radio base station apparatus, the user terminal comprising:

• a receiving section configured to receive a signal transmitted from the radio base station apparatus using a codebook that is set in advance in the radio base station apparatus to be uneven with respect to a direction of arrangement of antenna elements based on communication quality information of the user terminals in the cell;
• a channel quality measurement section configured to extract a reference signal from the received signal and measure channel quality;
• and
• a transmission section configured to feed back a communication quality feedback signal, including the measured channel quality, to the radio base station apparatus, via an uplink.

A radio communication method in a radio communication system comprising a radio base station apparatus to form a cell and user terminals to establish radio connection with the radio base station apparatus, the radio communication method comprising the steps of:

• at the radio base station apparatus:
• selecting precoding vectors from a codebook that is set in advance to be uneven with respect to the direction of arrangement of antenna elements, based on communication quality information of the user terminals in the cell;
• multiplying signals to supply to each antenna element by the selected precoding vectors;
• and
• transmitting the signals multiplied by the precoding vectors to the user terminals, at the user terminal:
• receiving a signal from the radio base station apparatus;
• extracting a reference signal from the received signal and measuring channel quality;
• and
• feeding back a communication quality feedback signal, including the measured channel quality, to the radio base station apparatus, via an uplink.